1. Field of the Invention
The present invention relates to a one-way clutch of roller type used as a part such as a torque transmitting element or a back stopper in a driving apparatus of a motor vehicle, an industrial machine and the like, for example.
2. Related Background Art
In general, a one-way clutch of roller type is comprised of an outer race having at least one pocket provided at its inner periphery with a cam surface, an inner race disposed in concentric with the outer race and having an outer peripheral track surface, a roller disposed within the pocket and adapted to transmit torque between the outer peripheral track surface of the inner race and the inner peripheral cam surface of the outer race, and a spring contacted with an idle rotation side of the roller.
With this arrangement, in the one-way clutch, the inner race is designed so as to be rotated only in one direction with respect to the outer race by means of a cam mechanism constituted by the roller and the cam surface. That is to say, the inner race is designed so that it is idly rotated relative to the outer race in one direction, and on the other hand, it applies rotational torque to the outer race via the cam mechanism only in an opposite direction.
For example, since a one-way clutch used as a starter of a motor bike is used under a high speed rotation condition and, thus, a great vibration condition and a severe condition in which the clutch is exposed to powder dust, foreign matters such as dust including worn powder are apt to be accumulated in the one-way clutch. Since the foreign matters accumulated in the one-way clutch affect a bad influence upon engaging performance, it is preferable to remove the foreign matters promptly in order to enhance the performance of the one-way clutch. Japanese Patent Application Laid-open No. 10-009292 (1998) discloses a one-way clutch of sprag type used as a starter of a motor bike and a method for removing foreign matters such as dust accumulated in a one-way clutch, in which grooves are formed in a side surface of an outer race and the dust is discharged via the grooves formed.
On the other hand, in the one-way clutch of roller type, to obtain positive engagement, the rollers as torque transmitting members and the springs for biasing the rollers must be prevented from being dislodged from the pockets in an axial direction and a radial direction.
Further, in order to enhance the performance of the one-way clutch, it has been proposed to lubricate the members. For example, in the above-mentioned Japanese Patent Application Laid-open No. 10-009292 discloses an arrangement in which a one-way clutch of sprag type used as a starter of a motor bike is lubricated by oil, and, in Japanese Patent Application Laid-open No. 5-044615 (1993) discloses an arrangement in which a starter clutch of roller type is lubricated by oil. On the other hand, some clutches are used under a dry condition without lubrication.
In comparison with the one-way clutch of sprag type, the one-way clutch of roller type has an excellent idle rotation endurance ability and does not generate malfunction due to roll over of the sprags (as is in the one-way clutch of sprag type) if a great load is applied; however, as is shown in the above-mentioned Japanese Patent Application Laid-open No. 5-044615, unlike to the one-way clutch of sprag type in which the engaging ability is enhanced by synchronous movements of the sprags by means of a cage of sprag type, in the one-way clutch of roller type, such an engaging ability cannot be enhanced and side plates for preventing dislodgement of the rollers and the springs must be provided, thereby preventing reduction in cost.
In this way, for example, as the one-way clutch used as the starter of the motor bike, it is desirable to obtain a one-way clutch of roller type which is cheaper in comparison with the conventional clutches and in which engaging reliability is more enhanced in comparison with the conventional clutches.